This invention relates to an image pickup device and its use in the inspection of packaged integrated circuits.
The development of high density, high speed integrated circuits has created the need for new approaches in packaging technology. Advanced package designs emphasize density of input/output lines, reduction in wiring length and reliability at the component level. Such high density designs use pin-pad arrays and other bonding approaches which sandwich the bonds between the chip carrier and the mother board. While this approach conforms to the needs of high density packaging, it creates quality control problems. Solder bonds in the final structure are hidden from view. Further, the multilayered ceramic carrier or mother board acts as a barrier to imaging or signal transmission techniques which might be applied to examine the solder bonds.
The problem of hidden bonds inspection has been in existence since the early 60's when the "Flip-Chip" package structure was successfully employed. Quality control of the flip-chip package was done by careful control of the bonding process rather than 100% visual inspection as needed to qualify the chip under Mil-Std 883B.
Until now, no known inspection technique existed to determine if solder bonds would meet the high reliability requirements for Military Standard 883B. Considering the electro-magnetic spectrum as well as particle beams there is potentially a large number of techniques capable of inspecting solder bonds. However, one important criterion must be immediately applied; the technique must not have the potential for generating failure in the device or in the associated packaging, thus eliminating penetrating radiation such as X-rays or neutrons used for radiography. Low energy radiation while not damaging the integrated circuit or the package fails to give clear results of possible defects occurring within the solder bonds. Electrical, acoustic, thermal and ultrasonic signals transmitted across the solder bond could reveal the absence of a bond. However, such techniques could not provide critical information about the size, contact angle of wetting, texture or other important information that is derived from direct visual imaging. These techniques suffer from problems of signal attenuations and modifications due to the complex composite structure of the package. These techniques also give rise to a concern about damage to the package or the device due to induced stresses.